In recent years, the ink-jet recording method has found wide application in photography, a variety of printing and in special printing, for example, marking and color filters, because it enables easy and low cost printing. Specifically, available is high image quality comparable to that of silver salt photograph, which has become possible by utilizing (i) an ink-jet recording apparatus in which ejection of minute droplets is controlled, (ii) an ink-jet ink exhibiting a wide range of color reproducibility, high durability and improved ejecting properties and (iii) an ink-jet recording sheet having drastically improved ink absorbing property, coloring property and surface gloss. Recent improvements in image quality of ink-jet recording methods have been achieved only by integrating ink-jet recording apparatus, improved ink-jet ink and improved ink-jet recording sheets.
However, an ink-jet system which requires a special ink-jet recording sheet is not fully recommended because the recording medium is limited and the cost for the recording medium increases. Therefore, many attempts of ink-jet recording have been made to print onto recording media other than special ink-jet recording sheets, the attempts include (i) a phase-change ink-jet recording method utilizing a wax ink which is solid state at ambient temperature; (ii) a solvent-type ink jet recording method in which a rapid-drying organic solvent is used as a main component of the ink; and (iii) an actinic ray curable ink-jet recording method in which the ink is cross-linked, after printing, by irradiating it with actinic rays, for example, ultraviolet (UV) rays.
Among these, an actinic ray curable ink-jet recording method has received close attention because of the relatively lower odor of the ink compared to that of a solvent-type. Actinic ray curable ink-jet recording methods have been disclosed, for example, in Japanese Patent Publication Open to Public Inspection (hereafter referred to as JP-A) Nos. 6-200204 and 2000-504778.
However, when these inks are employed, the dot diameter of the ink ejected onto the recording material tends to change depending on the kinds of recording material or operating conditions, and it is therefore relatively difficult to form a high resolution image on various recording materials.
Recently, many UV curable ink-jet recording methods using cationically polymerizable compounds have been proposed. UV-curable ink-jet ink is not affected by oxygen, however, it may have problems in that the polymerization reaction is affected by moisture or, under a certain curing condition, the printed ink wrinkles while shrinking in the process of polymerization.
As described above, an image forming method employing a UV curable ink-jet recording method enables low cost formation of high resolution images as well as image formation onto a recording material which does not absorb recording ink. However, this method also has problems which are characteristic for the UV curable ink-jet recording method. For example, when printing is carried out on a recording material which does not absorb the ink, a noticeable degradation of image quality may occur due to mixing of adjacent dots placed on the recording material. Specifically, when a high resolution image is required, mixing of dots of different colors may cause a big problem. In attempts to solve this problem, actinic ray curable ink-jet inks employing photo polymerizable oxirane compounds, vinyl ether compounds or oxetane compounds have been disclosed (for example in Patent Documents 1 and 2). Also, actinic ray curable ink-jet inks employing photo polymerizable alicyclic epoxy compounds or alicyclic oxetane compounds have been disclosed (for example in Patent Documents 3 and 4). However, even by employing the above mentioned methods, the problem of dot blur has not been fully overcome.
In the case of an aqueous ink-jet recording system, the problem of dot blur has been solved by improving the absorbability of the ink to the recording material by means of using a special ink-jet recording sheet or using additives to the ink having various functions, however, in the case of the ink-jet recording system in which the recording material does not have absorbability of the ink, it is relatively difficult, at present, to find an adequate answer to fully overcome the problem. Specifically, in the case of a high rate printing, the recording material after printing tends to be rolled up in a roller, accordingly, development of an actinic ray curable ink-jet ink exhibiting a rapid curing property is desired.
(Patent Document 1)                JP-A No. 2001-220526        
(Patent Document 2)                JP-A No. 2002-188025        
(Patent Document 3)                JP-A No. 2002-317139        
(Patent Document 4)                JP-A No. 2003-55449        